1. Field of the Invention
The present invention relates to an actuator device, such as a hydraulic control device in which an actuator is installed, a control system and a method for the actuator device.
More particularly, the present invention relates to an actuator device, such as a hydraulic device, applied to, for example, an internal combustion engine, such as a diesel engine, a control system and a method for the actuator device.
2. Description of the Related Art
Conventional actuators that energization can make operate include an actuator, such as a piezoelectric actuator, a magnetostrictive actuator, or the like, which deforms according to amount of energy based on the energization and kept by itself, thereby generating driving force, such as pressing force. Conventional actuator devices in each of which the above actuator is installed, such as, hydraulic control valves, fuel injectors and so on, are proposed.
The actuator devices are applied to, for example, a common-rail fuel injection system of a diesel engine. The actuator of each actuator device is used for generating driving force to a needle for changing the fuel injection system between a state of injecting fuel and that of stopping the injection of fuel.
The actuator of each actuator device applied as a hydraulic control valve to a common-rail fuel injection system of a diesel engine is also used for driving a valve member so as to control a fuel pressure in a back pressure chamber formed in a back side of the needle, thereby changing a displacement of the needle.
With the actuator device applied as the hydraulic control valve, the valve member is configured to close one of a high pressure port communicated with a pressure accumulator referred to as “common rail” and a low pressure port communicated with a drain passage, thereby controlling a fuel pressure in the back pressure chamber, which is supplied as high pressure to the needle.
That is, the actuator operates so that the valve member makes open the low pressure port and close the high pressure port, causing the fuel pressure in the back pressure chamber to drop, thereby lifting the needle. The lifting operation of the needle causes the fuel to be injected through an injection hole of the hydraulic control valve. The actuator also operates so that the valve member makes open the high pressure port and close the low pressure port, causing the pressure in the back pressure chamber to rise again. The rise of the back pressure causes the needle to drop, thereby interrupting the injection of fuel.
In these fuel injection systems, the actuator operates so as to change the driving force or the fuel pressure with respect to the needle, so that the injection timing of fuel or injection quantity thereof is determined by the changing timing of the actuator's operation. An ECU (Electric Control Unit) controls the changing timing of the actuator's operation.
In the described common-rail fuel injection system, in order to carry out the fuel injection according to the operating state of the engine, it is important to improve the controllability of a fuel injection pressure (common rail pressure) and a fuel injection rate (fuel injection quantity unit of time). The quantity of fuel delivered to the common rail by a high-pressure pump usually controls the common rail pressure, and a special depressurization valve provided for the common rail controls the common rail pressure according to the abruptly requirement of depressurizing the common rail pressure. Recently, however, it is examined to carry out the depressurization control through the hydraulic control valve without providing the special depressurization valve. This depressurization control can be performed by moving the valve member of the hydraulic control valve up to a middle (half) position between the low pressure port and the high pressure port, causing the fuel in the common-rail to be relieved. In addition, the hydraulic control valve permits the valve member to be located between the low pressure port and the high pressure port, making it possible to easily control the pressure in the back pressure chamber. It is expected to accurately inject a small amount of fuel and to improve the performance of the fuel injection system.
Variations of the performances of actuator devices are generated among each other due to the unevenness among the designs or qualities of the manufactured actuator devices.
Even when, therefore, energizing the actuators of the actuator devices at the same timing, the timings of fuel injections of the actuator devices or the quantities of fuel thereof, which are injected therefrom, are relatively different from each other, so that it is impossible to completely handle a requirement for decreasing exhaust gases in recent years and other similar requirements. Then, one approach for solving the problem related to the variations of the actuator devices is disclosed.
That is, as described in the U.S. Pat. No. 5,634,448, this approach is to previously measure injection characteristics of the injectors, respectively, so as to correct, according to the measured injection characteristics, operating parameters of each of the actuators of the injectors, operator parameters which determine the operation timing and the operation time of each of the actuators thereof. The offset values of the operator parameters are written onto a memory or the like of the ECU so that the ECU reads the offset parameters from its memory. The writing of the offset value onto the memory or the like is performed by scanning the offset value which is bar-coded to the corresponding injector to which the measurement of the offset value is already completed, thereby writing the scanned offset value onto the memory.
However, the above conventional fuel injection system requires the great energy to lift from the low pressure port the valve member subjected to the fuel pressure in the high pressure port. In addition, when the valve member once lifts, the fuel pressure is also applied to the valve member in the lifting direction. The requirement of the great energy and the application of the fuel pressure in the lifting direction make it extremely difficult to control stably the valve member so as to keep it at a half-lift position between the low pressure port and the high pressure port.
In the present circumstances, therefore, it is hard to carry out the half-lift control of the valve member in the conventional fuel injection system to which the hydraulic control valve with the above described configuration is applied.
In addition, in cases where the operating characteristics of actuators themselves determine the operating conditions of some actuator devices in which the actuators are installed, respectively, the operating conditions of some actuator devices do not very vary among each other. In cases where each of other actuator devices has a complicated configuration, such as the above injector, or each of which contains hydraulic pressure interposed between the actuator and the valve member or the needle, the operating conditions of the other actuator devices easily vary among each other.
For example, in a part of injectors, the pressing force of the actuator required for moving the valve member or the needle away from the position at which the valve member or the needle is seated is relatively insufficient, causing the seat of the valve member or the needle to be instable. In this case, it is considered to set the quantity of energy delivered to the actuator to sufficiently great one enough for the movement of the valve member or the needle away from the seated position, making it possible to secure the pressing force required for the movement of the valve member or the needle.
However, in some actuator devices, such as engines performing a greatly number of fuel injections, whose actuators frequently operate, delivering excessively great quantity of energy to the actuators causes a heavy energy loss. Moreover, delivering excessively great quantity of energy to the actuators also causes heat generation in some actuator devices, and causes excessive wear of each component of some actuator devices to be accelerated. These problems bring about variations of the injection characteristics of the injectors with time, so that even when adopting the techniques described in the U.S. Pat. No. 5,634,448 to the actuator device, it is not necessarily to perform fuel injection with a high degree of accuracy.